Run your retirement plan 1,000 times.
A Monte Carlo simulator runs your plan against 1,000 different market histories instead of one optimistic guess, so you see the odds your money actually lasts. No signup, nothing collected, it runs entirely in your browser.
How the simulation works.
This calculator does not reduce to a single closed-form formula; it is a stochastic simulation, so this section explains how the simulation works rather than presenting a step-by-step equation. The three asset-mix mean and standard-deviation return assumptions (conservative 2.5% / 6%, balanced 4.5% / 11%, aggressive 6.5% / 16%) are working placeholders pending CFP/CPA review. They are intentionally on the conservative end of long-run history to avoid overpromising outcomes.
Assumptions
- Returns are normally distributed and independent year to year. Real markets exhibit fat tails and serial dependence (momentum, mean reversion).
- Three asset-mix return assumptions are working placeholders. No CFP or CPA has reviewed them.
- Contributions stop and withdrawals begin at the retirement age you enter; both happen in a single annual lump.
- Withdrawals are a constant annual nominal dollar amount (no inflation adjustment, no variable spending policy).
- No taxes on contributions, growth, or withdrawals. Real outcomes depend on account type (Roth vs Traditional) and tax bracket in retirement.
- No Social Security, pension, or other income streams during retirement.
Limitations
- Normal-distribution returns underestimate the frequency of extreme years; real history has fatter tails.
- Sequence-of-returns risk (bad years EARLY in retirement) is captured by the simulation but not flagged separately; the success-rate number alone hides this.
- 1,000 trials is enough for stable summary statistics but the tails (the worst 50 outcomes) can still vary between two runs of the same inputs unless the random seed is fixed.
- No inflation modeling. A 4% nominal balanced return is meaningfully smaller in real (after-inflation) terms.
- No glide-path modeling (gradually shifting from aggressive to conservative through working years and retirement).
- It is not a forecast of any specific market's actual return.
- It is not a retirement plan. A real plan handles Social Security claiming, tax-deferred vs Roth withdrawal sequencing, healthcare costs, and changes in spending over decades.
- It is not personalized advice. The asset-mix return assumptions are placeholders pending CFP/CPA review; the success-rate number can shift meaningfully when those numbers are revised.
- It is not a substitute for an actual retirement professional for households where the answer matters.
Common questions.
What is a Monte Carlo simulation?
A Monte Carlo simulation runs the same plan many times, drawing a different set of random market returns on each run. Instead of one guess about the future, you get a range of outcomes and can see how often the plan holds up. This tool runs your retirement plan 1,000 times that way.
Is this Monte Carlo retirement calculator free?
Yes. The Retirement Reality Check is free to use, with no signup and no account. It runs entirely in your browser and collects nothing.
The three fundamentals under the hood.
The Retirement Reality Check rests on three fundamentals. Each one has its own plain-English lesson.
Compound growth. Why the same yearly return turns small contributions into large balances over decades, and why starting earlier matters more than starting larger.
Emergency fund. Sequence-of-returns risk is hardest to absorb early in retirement. A buffer of cash that does not depend on the market is the simplest defense.
401(k) basics. The most common vehicle for the "Adding each year" input in this tool. How contributions, employer match, and vesting actually work.
Educational simulation only. The asset-mix return assumptions are working placeholders pending CFP/CPA review, and the success-rate number can shift meaningfully when those numbers are revised. This tool models no taxes, no inflation, and no Social Security or pension income. ClearMoneySchool does not provide personalized financial or retirement advice.